The present disclosure relates generally to plasma etch processes and, more specifically, to the plasma etch processes used in the manufacture of integrated circuits, MEMS (micro electronic machines), and flat panel displays.
Integrated circuits include many layers (for example, oxides, nitrides, polycrystalline silicon, single metal films, sandwich stacked metal films, and other materials) that require plasma etching. Since integrated circuits are to be as planar as possible, there are etching processes that take place which require the ability to selectively etch one material compared to the other in order to produce planarization. Plasma etching includes introducing a reactant gas into the chamber and forming a plasma etching by applying an energy source. Depending upon the gases, a carrier or a strike gas may be included. The strike gas is that which is responsive to the applied rf energy at a low enough pressure to create a plasma which then results in breakdown of the reactant gases to radical reactants which then selectively etch one material more than another.
The reactant gases, with or without the carrier gas, are introduced into the plasma chamber at a given flow rate and proportion. The resulting plasma etches the surface of the target within the chamber, which generally is a wafer with a plurality of dies or integrated circuits. Below the target is an exhaust valve connected to turbo and roughing pumps by a throttle valve. The roughing pump brings the pressure low enough to allow the turbo pump to be turned on. The turbo and roughing pumps and throttle valve in combination control the removal of by-products. A control system including a Baratron (pressure transducer) controls the opening of the throttle valve to maintain a constant pressure in the chamber and an even exit flow. An example is shown in FIG. 1.
Although the present disclosure has examples using the Applied P5000 Etcher of Applied Materials, other models and other manufacturers' etchers may be used. The etch processes have been set up based on varying etch gas flows, varying pressure and varying throttle valve opening values to achieve a desired etch rate and desired levels of non-uniformity of etching as measured on a pilot process. This is not done on a product or product line basis. Non-uniformity creates areas or dies within the wafer, which either must be re-worked or scrapped totally. The ones that are underetched are capable of being re-worked, but those that are overetched must be scrapped. Where one or more reactant gases are used, it is desirable that the adjustability of the ratio between and/or the flow rate of the two gases be as large as possible within the constraints of the selectivity and non-uniformity criteria. The quantity and flow rate and throttle valve settings used in the pilot programs are not always applicable in the production line fabrication.
The throttle valves are generally set in a range below 25 steps of an 800-step fully-opened valve. When the turbo pump surges, the system cannot adequately control the low gas flows within the etching chamber and, therefore, leads to non-uniform etching. The exhaust port at one side of the etching chamber makes the etching chamber very sensitive to rapid changes of flow and limits the ability to maintain uniformity across the etching chamber.
The present disclosure is a method of operating a plasma etcher wherein gas is introduced into the etcher at a substantially higher rate than a previous standard rate for a desired etch selectivity, and the throttle valve's open value is set to a substantially greater open value than a previous standard open value for the desired etch selectivity. The rate is increased by at least, approximately twice, and the throttle valve's open value is increased by at least, approximately four times. The method may also include introducing the gas at a lower pressure than the pressure of the previous standard pressure for a desired etch selectivity. The pressure is reduced by at least, approximately one-half.
The method reduces the non-uniformity of etching in and/or increasing the flow rate window of the gas in the plasma etcher for a desired etch selectivity.
An electrical device made from a process including the disclosed etching steps include one or more of an integrated circuit, micro electronic machines and flat panel displays.
A plasma etcher according to the disclosure includes a chamber with a gas inlet for at least one gas and an exhaust port, an rf energy applicator for creating a plasma, and a throttle valve connecting the exhaust port to a pump. A control system introduces the gas into the chamber at a substantially higher rate than a previous standard rate for a desired etch selectivity and sets an open value of the throttle valve to a substantially greater open value than a previous standard open value for the desired etch selectivity.
The plasma etcher may include a first throttle valve connecting the exhaust port to a first pump via a first conduit; and a second throttle valve connecting the exhaust port to a second pump via a second conduit. The first conduit has a larger diameter than the diameter of the second conduit. The control system operates the opening of the first throttle valve for a dry cycle after a cleaning cycle of the etcher and operates the opening of the second throttle valve during an etching cycle.
These and other aspects of the present disclosure will become apparent from the following detailed description of the disclosure, when considered in conjunction with accompanying drawings.